1Far Eastern Federal University, School of Natural Sciences
2 Far Eastern Federal University, Oriental Institute School of Regional and International Studies
aкekck96@mail.ru
It is generally known that plants require sunlight for photosynthesis, but not everyone knows that sunlight also plays an important role in regulating life cycle of plants. Red light affects a pigment called phytochrome (from phyton – plant and chroma – colour) [3]. Phytochrome system enables plants to react on property, intensity and duration of solar illumination by changing processes of growing and shape development called photomorphogenesis [5]. Identification of photopigments is a primary task when studying mechanism of photoregulating reactions. However, pigments of the majority of photoregulating processes are still not identified, the exception is phytochrome. Due to discovery of this pigment the studies of the mechanism of photoregulating reactions advanced dramatically.
The purpose of the paper was to establish the role of phytochrome and the mechanism of its participation in photoregulating reactions of plants. The tasks of the work were
1. To examine the structure and peculiarities of phytochrome system functioning;
2. To elicit correlation between the phenomenon of photoperiodism and phtobiological function of phytochrome;
3. To determine regulating role of phytochrome in photomorphogenetic reactions
4. To cover main perspectives and problems of studying phytochrome.
The literature review let us come to following conclusions.
Phytochrome is a chromoprotein. Its optical properties and ability to act as a photoreceptor are determined by chromophore which is a linear tetrapyrrol. The characteristic property of phytochrome is its photoreversibility and the presence of two interconvertible forms [2]. One form is blue in color and has the absorption maxima at 660 nm (red – Pr), whereas the other form is olive-green in color and absorbs maximally at 730 nm (far red – Pfr). On exposure to red light (660 nm), the Pr form is converted to the Pfr form, which is considered as the biologically active form. The Pfr form is converted back to the Pr form on absorption of far-red light (730 nm). The phytochrome molecules have dual roles which are sensory and regulatory. Phytochromes sense the light environment, undergo a photoconversion and transduce the signals through signaling pathways, which ultimately lead to regulated gene expression and appropriate morphogenesis (Fig. 1). Light-induced formation of physiologically active form of phytochrome is also connected with structural reorganization of membranes [4]. The state of phytochrome can regulate formation and amount of four types of hormones: ethylene, cytokinins, auxin and gibberellins.
Fig. 1. The boundary conditions of task
The relative lengths of light and dark periods of day during the year have a strong influence on plants vital functions. The physiological reaction of organisms to the change of the length of day or night is called photoperiodism. In relation to photoperiod there exist long-day plants and short-day plants. To begin flowering short-day plants need less biologically active phytochrome, absorbing far-red rays, while long-day plants need a greater content of it.
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Phytochrome triggers photomorphogenetic reactions of plants like de-etiolation of seedlings, which were grown in dark, stimulation of seed germination, start of flowering, shade avoidance and switch to dormant state [1].
The scientists reported to have approached the control of genes activity by light flashes. In this reaction the main role belongs to the phytochrome pigment. This technology offers the challenge in areas like producing bio-fuel and antibiotics as well as in genetic engineering. In the future, it should be possible to modify agricultural crop plants with genetically improved phytochrome molecules (such as decreased shade avoidance and red-shifted absorbance maxima) using information gathered from studies of a detailed structural-function map for phytochrome [2]. The scientific interest to phytochrome grows steadily. For years, there has been debating about the intracellular localization of phytochrome. Early studies supported the notion that phytochromes are localized outside the nucleus. Recently, it was shown that they can translocate from cytoplasm into the nucleus [2]. The molecular machinery of phytochrome system action has not still been revealed completely, but new reports appear in scientific literature regularly. These reports let us come nearer to understanding of this important phenomenon in life of plants.
References:
1. Chernova, N.M. General ecology / N.M. Chernova, A.M. Bylova. — M.: Drofa, 2004. — 412 p.
2. Galston, A. The life of the green plant. – M.: Mir, 1983. – 552 p.
3. Haiyang, W. Phytochrome Signaling Mechanism / W. Haiyang, W.D. Xing // American Society of Plant Biologists. – 2002. – P. 25-30.
4. Kulaeva, O.N. How light regulates the life of the plant// Sorovskiy educational journal. – 2001. – Book 7. – №4. –P. 6-12.
5. Warring, P. The growth of plants and the differentiation / P. Warring, I. Phillips. – М.: Mir, 1994. – 512 p.